Because integrated circuits are so small, microscopes, such as metrology systems, are typically used to view them. The metrology systems that the various embodiments of the present invention apply to include scanning microscopes such as, for example, high resolution profilers, atomic force microscopes, scanning tunneling microscopes, scanning electron microscopes, near-field scanning optical microscopes, and other means of surface observation that build up magnified images of the sample in a line by line raster fashion. All such applicable microscopes are generally referred to herein as microscopes.
Unfortunately, there is a drift that occurs when there is undesired motion between the observing component of the microscope and the sample that is being observed by the microscope. The observing component is a probe tip in microscopes such as high resolution profilers, atomic force microscopes, scanning tunneling microscopes, and near-field scanning optical microscopes, or an electron beam in microscopes such as scanning electron microscopes.
The drift error that is often observed in these measurements may be due to a number of factors, including but not limited to differential thermal expansion between the sample and various components of the microscope, and mechanical creep of the microscope components in the mechanical loop between the observing component of the microscope and the sample.
The current industry practice to reduce this drift error is to design the moving components of the mechanical loop in such a way as to minimize the drift, such as by having more precision components in the mechanical loop. Unfortunately, as magnification increases, even such high precision components tend to have at least some amount of positional drift. Further, over time, even the best mechanical components will tend to wear to some extent, thus increasing the drift that is inherent in such mechanical components.
Other so-called solutions to this problem require that the microscope collects an image of the sample, and then uses software to recognize features within the image to adjust the scan for a subsequent scan. However, these approaches require multiple scans of the image, which takes more time.
What is needed, therefore, is a system for reducing problems such as those described above, at least in part.